This invention relates to a power transmission belt and method for fabricating the same, and particularly relates to a power transmission belt such as a V-ribbed belt or a V-belt including short fibers mixed into its compression rubber and a method for fabricating the same.
As disclosed in Japanese Patent Application Laid-Open Gazettes Nos. 3-219147 and 7-4470, there are conventionally known power transmission belts in which a crowd of short fibers are mixed into their compression rubber in a manner to be oriented along the width of the belt and some of the short fibers are extruded from the surface of the compression rubber. Power transmission belts of such kind aim at enhancing bearing strengths and wearing properties of their friction drive sections and preventing noise production during their running.
However, even such a power transmission belt out of which some of the short fibers extrude, if the total area of extruded sections of the short fibers occupying the surface of the compression rubber is small, cannot enhance its wearing property so much because the area of the compression rubber in direct contact with a pulley becomes correspondingly large.
For the purpose of increasing the exposure areas of short fibers with respect to the surface area of the compression rubber, Japanese Patent Application Laid-Open Gazette No. 1-164839 has proposed a power transmission belt as shown in FIG. 19. In this power transmission belt, extruded sections 102 of short aramid fibers 101 mixed into a compression rubber 100 are 0.065 to 0.13 mm long, longer than those of conventional short fibers, and are bent in a particular direction 103 along a working flank of the belt.
In such a power transmission belt, though the exposure areas of short fibers 101 can be increased, the extruded sections 102 are bent at their roots and therefore made substantially flush with the surface of the compression rubber 100. Accordingly, the extruded sections 102 are difficult to together form surface unevenness as considered as effectively suppressing noise. This invites a problem that the effect of suppressing noise cannot sufficiently be obtained.
Furthermore, since the extruded sections 102 of short fibers are bent in the particular direction 103 along the surface of the compression rubber 100, running the belt in a reverse direction would largely change properties of the belt. Therefore, in order for the belt to obtain its properties as designed, the belt must be checked carefully on its running direction at the time of fitting to pulleys. In addition, this conventional belt is not applicable to devices capable of conveniently switching the running directions of the belt.
Moreover, if the length for which the short fiber is extruded from the surface of the compression rubber 100 is too large, the belt will largely change its properties when the extruded sections 102 are reduced by abrasion. Therefore, considering to maintain desired belt properties constant for a long time, there is a limit to the extruded length of the short fiber. Accordingly, it has been desired to make great strides in enhancing the performance of the belt by improving not only short fibers but also the compression rubber 100.
In view of these problems, an object of the present invention is to provide a power transmission belt excellent in wearing property, hard to produce noise and independent of its running direction.
Another object of the present invention is to further enhance the performance of the belt by improving the surface configuration of the compression rubber.
To attain the above first object, a power transmission belt of the present invention is constructed so that extruded sections of short fibers are formed in curled shape.
More specifically, a power transmission belt of the present invention is directed to a power transmission belt in which a crowd of short fibers are mixed into a compression rubber thereof in a manner to be oriented in a given direction and some of the short fibers each have an extruded section extruded from a surface of the compression rubber, and is characterized in that the extruded section of the short fiber is raised from the surface of the compression rubber and then bowed.
With this construction, since the extruded sections of the short fibers are bowed, they have sufficiently large exposure areas with respect to the surface area of the compression rubber, resulting in enhanced wearing property of the compression rubber. Further, since some of the short fibers are raised from the surface of the compression rubber, their root portions are not born against but kept off from the surface of the compression rubber. Accordingly, microscopic unevenness is formed over the surface of the compression rubber so that the root portions of short fibers constitute microscopic convexities, thereby suppressing the occurrence of noise.
The extruded section of the short fiber is preferably bowed first in one direction and then another direction on the way from root to tip thereof.
With this construction, when the belt is entrained about a pulley, the short fibers exert restoring forces like a leaf spring on the pulley. As a result, the restoring forces can absorb variations in belt tension associated with the running of the belt. Accordingly, the belt can transmit power with stability, i.e., the belt can stabilize its power transmission performance. Also, though the pressures to be applied to the short fibers will become larger with increase in bearing stress on the surface of the compression rubber, the stresses placed on the root portions of the short fibers can be relaxed by the restoring forces of the bowed portions of the short fibers. Accordingly, the short fibers can be prevented from dropping out of the compression rubber, which enhances the wearing property and elongates the life time of the belt.
At least the tip of the extruded section of the short fiber is preferably flattened. In this case, the surface area of each short fiber can be increased thereby enhancing the wearing property of the belt.
The tip of the extruded section of the short fiber may be cracked. Also in this case, the surface area of each short fiber can be increased thereby enhancing the wearing property of the belt.
The extruded sections of the short fibers are preferably different in bowing direction from one another to decentralize the orientation thereof.
With this construction, since the extruded sections of the short fibers are different in bowing direction from one another to decentralized their orientation, this makes it possible to exhibit the wearing property of the belt uniformly in every direction. Therefore, even if the belt is run in a reverse direction, its properties do not change. In other words, the belt has no dependency on its running direction. Accordingly, the compression rubber of the belt can exhibit uniform bearing strength and wearing property in either running direction independent of the running direction of the belt.
The short fiber may be made of para-aramid fibers or meta-aramid fibers. In these cases, suitable short fibers can be obtained.
To attain the above second object, a power transmission belt of the invention is constructed so that unevenness is provided in the surface of the compression rubber to increase its entire surface area.
Specifically, in the power transmission belt, the surface of the compression rubber is preferably formed in uneven configuration.
With this construction, since the surface of the compression rubber is formed unevenly, its entire surface area can be increased. This enhances the performance of the belt. In addition, clearances are likely to be formed between contact surfaces of the belt and a pulley. Accordingly, even if water or the like enters between the belt and pulley, it can be distributed or discharged through the clearances, which stabilizes frictional resistance of the belt.
The surface unevenness of the compression rubber is preferably formed in wavy shape. Thereby, a suitable uneven configuration can be formed in the surface of the compression rubber.
The surface unevenness of the compression rubber is preferably formed to have a level difference of 0.5 to 10 xcexcm. Also in this case, a suitable uneven configuration can be formed in the surface of the compression rubber.
A method for fabricating a power transmission belt of the present invention is directed to a method for fabricating a power transmission belt in which some of a crowd of short aramid fibers are extruded from a surface of a compression rubber, and is characterized by comprising the step of grinding the compression rubber into which the crowd of short aramid fibers are mixed in a manner to be oriented in a given direction with a grinding wheel having super abrasives extruded for 50 to 95% in grain size thereof from the surface of the grinding wheel.
According to this method, since the height of extrusion of each of the super abrasives is large, a bonding part for the super abrasives in the grinding wheel is prevented from direct contact with the compression rubber of the power transmission belt, there by suppressing production of frictional heat. Accordingly, the grinding step can be carried out under extended conditions such as increase in the grinding speed. Further, the length for which each of the short aramid fibers is extruded from the surface of the compression rubber can be easily increased. This facilitates the bowing of the extruded sections. In addition, such a large height of extrusion of the super abrasive can facilitate to form the surface of the compression rubber into uneven configuration.
Another method for fabricating a power transmission belt of the present invention is also directed to a method for fabricating a power transmission belt in which some of a crowd of short aramid fibers are extruded from a surface of a compression rubber, and is characterized by comprising the step of grinding the compression rubber into which the crowd of short aramid fibers are mixed in a manner to be oriented in a given direction with a grinding wheel having super abrasives the density of which is 3.5 to 55%.
According to this method, since the density of the super abrasives is small, chip pockets can be increased so that grinding chips can be readily expelled. Therefore, clogging between the abrasives due to the chips is difficult to occur. Accordingly, it can be suppressed that such clogging increases grinding load and produces heat in a grinding surface. As a result, the grinding step can be carried out under extended conditions. Further, since the short aramid fibers extruded out of the compression rubber are hardly cut, this facilitates the formation of extruded fiber sections of long length and the bowing of the extruded fiber sections. In addition, such a small density of the super abrasives can facilitate to form the surface of the compression rubber into uneven configuration.
Still another method for fabricating a power transmission belt of the present invention is also directed to a method for fabricating a power transmission belt in which some of a crowd of short aramid fibers are extruded from a surface of a compression rubber, and is characterized by comprising the step of grinding the compression rubber into which the crowd of short aramid fibers are mixed in a manner to be oriented in a given direction with a grinding wheel having super abrasives which are each extruded for 50 to 95% of grain size thereof from the surface of the grinding wheel and the density of which is 3.5 to 55%.
According to this method, since the height of extrusion of each of the super abrasives is large and the density thereof is small, increase in grinding load and heat production in a grinding surface can be suppressed. Accordingly, the grinding step can be carried out under extended conditions. Further, it can be facilitated to increase the length for which each of the short aramid fibers is extruded from the surface of the compression rubber and bow the extruded fiber sections. In addition, since the density of the super abrasives is small, chip pockets are large in size so that grinding chips can be readily expelled. Therefore, clogging between the abrasives due to the chips is difficult to occur.